Noguchi et al. developed alternative collision operators for MPCD fluids.
They
use a Langevin or Anderson thermostat
to
keep
temperature
constant
but also
to
conserve momentum
locally
[1]}, [2]}.
Thus,
a canonical ensemble of fluid particles is modeled,
where energy
is
conserved on average.
An advantage of
these alternative
collision rules is that local angular momentum conservation,
which is missing in the original SRD formulation, can be included in a rather simple way.
Although angular momentum conservation does not directly alter the Navier Stokes equations,
it ensures that the stress tensor is symmetric,
as it should be for the
Newtonian
fluid with its isotropy. Indeed, it
has
been shown that neglecting angular momentum conservation in the fluid may lead to
incorrect physical effects [3]}.
One popular approach
for the collision operator
is to use the Anderson thermostat
and, in addition, conserve
angular momentum.
This type of collision rule is
abbreviated by MPC-AT+a [1]}.
It
has
widely
been used
to study the dynamics of squirmers in MPCD fluids
[5]}, [6]}, [7]}, [8]}, [9]}, [10]}, [11]}.
